The present invention relates to a chassis arrangement having a steerable element, in particular a wheel, steerable on tilting of said chassis relative to the ground, and to a steerable element for use in a chassis.
A chassis arrangement having a steerable element which is steerable on tilting of the chassis relative to the ground is known from international application No. WO 88/04565.
In this known chassis arrangement the steerable element is mounted on the chassis via first and second links. The first link is pivotally supported at one end on said chassis and supports a substantially horizontally disposed axle for said steerable element, and the second link is pivotable about an axis disposed parallel or oblique to the ground and substantially intersecting the contact area, where, in the straight ahead position of the steerable element, the latter contacts the ground. In addition means is provided between said first and second links defining a substantially vertical axis which substantially intersects the first said axis at said contact area, and the steerable element is swivellable about this vertical axis to effect steering on pivotal movement of said second link about the first said axis under the moment created by the ground pressure and its moment arm about the first said axis resulting from tilting of the chassis.
The known chassis (international application publication No. WO 88/04565) is particularly envisaged for use with a roller skate, a skateboard, a roller ski, a roller bob, a snow scooter or the like, i.e. with devices where steering is produced as a result of displacement of the user's weight resulting in tilting of the chassis. Since the steering element can have different forms, for example a wheel in a roller skate or skateboard, a caterpillar type device in a dry ski, or a ski, slid or mow device in a snow scooter, this term will be understood whereever it is used in the specification, to cover any of the relevant items, depending on the particular construction of the device involved.
The aforementioned international application publication No. WO 88/04565 describes in detail the possible scope of application of such a chassis and the fact that it is applicable to one or two track vehicles, for example to a so-called in-line skate having two or more wheels arranged in a line one behind the other, or to a roller skate of a more conventional appearance with pairs of wheels arranged on each axle. The thoughts expressed in this respect in the aforementioned international application concerning the wide applicability of the chassis design are equally relevant here.
The kinematics of a chassis of the above described kind are such that frictional forces acting sideways on the steerable element or wheel have substantially no effect on the steering, since they have no moment arm about either of the relevant axes, i.e. the first said axis or the vertical axis. In straightahead running the reaction force at the contact patch also has substantially no moment arm about either of the said axes, since it acts substantially vertically through the vertical steering axis. Thus the reaction force also has no relevant moment arm which could induce a steering moment. If, on the other hand, the user displaces his weight so that the chassis is tilted relative to the ground, the reaction force of the ground is moved sideways so that it now has a moment arm about the first said axis. This results in a small pivotal movement of the specially cranked second link about the first said axis so that the end of the second link adjacent the steering element moves sideways. This in turn rotates the first link about its point of mounting on the chassis, resulting in rotation of the steerable element or wheel about the vertical axis and a steering movement to the right or left depending on the direction of tilting of the chassis. Tilting of the chassis to the left results in steering to the left and vice versa. The amplitude of the steering movement is related to the amplitude of the tilting movement.
A problem arises with a chassis of the kind known from international application No. WO 88/04565 in as much as the connection between the first and second links defining the vertical axis is positioned above the steerable element or wheel and requires a certain amount of space. It is however known from experience of roller skates and the like that the lower the chassis can be made the easier it is for the user to skate thereon. Even a reduction in height of as little as 1 cm has a substantial influence on the behaviour of the skate.
It is accordingly a first object of the present invention to so further modify the chassis design of the above-mentioned kind that an extremely compact chassis is obtained, in particular a chassis having an overall height which is reduced to a minimum, with the task of manufacturing the chassis being kept straightforward and with the cost of the individual components and of the chassis being minimised. Moreover, the chassis should be easy to assembly and reliable in use.
It is a further object of the present invention to provide an improved steerable element for use in a chassis, in particular a steerable wheel which can be substituted for existing non-steerable wheel assemblies in in-line skates and the like to convert the same to more readily steerable skates, in particular skates capable of describing circular arcs.
A yet further object of the present invention is to provide a wheel and axle assembly which could be mounted on a supermarket trolley to make the same more easily steerable.